1. Field of the Invention
This invention relates to a composition curable by active energy rays such as ultraviolet light, electron beams or radioactive rays, and particularly to a composition which is suitably used as an adhesive in the production of optical discs.
2. Description of the Prior Art
Photocurable compositions are known. For example, Japanese Laid-Open Patent Publication No. 51035/1973 discloses an ultraviolet light-curable composition comprising (a) at least one oligo ester which is selected from the group consisting of polyester acrylate, polyester methacrylate, epoxy acrylate and epoxy methacrylate having a boiling point at atmospheric pressure of at least 200.degree. C. and has an acryloyl group content of 5 to 100 mole % based on the total amount of the acryloyl and methacryloyl groups, (b) a sensitizer and (c) a thermal polymerization inhibitor. The patent document describes ##STR2## as the component (a). However, when an ultraviolet light-curable composition obtained by using this component is used as an adhesive, it has low tensile shear peel strength and tensile adhesion strength.
U.S. Pat. No. 4,150,170 describes a method of producing an ultraviolet light-curable pressure-sensitive adhesive using an ultraviolet light-curable pressure-sensitive composition comprising an alpha, betaethylenically unsaturated vinyl polymerizable monomer and a benzoin C.sub.1 -C.sub.12 hydrocarbon alkyl ether. For example, Example 1 of this patent describes a method in which compositions containing butyl acrylate, vinyl acetate and acrylic acid as the above monomer is used.
Japanese Laid-Open Patent Publication No. 142070/1950 discloses a photosensitive adhesive consisting predominantly of a mixture of
(A) 100 parts by weight of a polymeric substance containing acryloxy or methacryloxy groups represented by the following formulae (I) to (III) in the molecule ##STR3## wherein R represents a hydrogen atom or a methyl group, n represents an integer of 2 or 3, m is an integer of 1 to 4, and l is an interger of 1 to 30, said polymeric substance being obtained by the addition-reaction of a polymeric substance having an unsaturated double bond in the molecule with an acrylic compound containing a carboxyl or hydroxyl group in the presence of an alkyl hypohalite or an N-haloamide compound, and
(B) at least 50 parts by weight of cyclohexyl methacrylate. This patent document describes an example in which methacrylic-modified polybutadiene is used as the polymeric substance containing an acryloxy or methacryloxy group.
In the prior art, optical discs are produced by bonding a recording layer provided on a substrate and a light-pervious protecting material by means of a photocuring agent. A photocurable composition which can be used in this application is desirably required to have excellent tensile shear peel strength and tensile adhesion strength, effect bonding within a short period of time, and be free from components that adversely affects the recording layer, and further not to impair the optical properties such as transparency of the substrate.
Photocurable compositions known heretofore do not sufficiently satisfy all of these properties.